Surface-Grafted, Covalently Cross-Linked Hydrogel Brushes with Tunable Interfacial and Bulk Properties
Surface-Grafted, Covalently Cross-Linked Hydrogel Brushes with Tunable Interfacial and Bulk Properties
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DOI：
10.1021/ma2006443
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发表时间：
2011-07-12
期刊：
影响因子：
5.5
通讯作者：
Spencer, Nicholas D.
中科院分区：
文献类型：
--
作者：
Li, Ang;Benetti, Edmondo M.;Spencer, Nicholas D.
将大分子连接到表面是一种对有机和无机材料进行功能化、保护和结构化的通用方法。本研究采用UVLED引发的光聚合方法，在硅基上制备了聚丙烯酰胺(PAAM)刷子和共价交联水凝胶刷子薄膜，并用多种分析方法对其性能进行了研究。所采用的光接枝方法允许在水环境中控制地制备非常厚的薄膜(最大可达1微米)，聚合时间不到1小时，并且没有副反应。通过向反应容器中加入微量的交联剂双丙烯酰胺(高达1.0wt%的单体溶液)，制备了PAAM共价交联水凝胶刷子。接枝聚合物链的侧向交联度对聚合物膜的本体和界面性能都有很大的影响。与理论预期一致的是，随着交联度的增加，聚合物刷的构象自由度减少，导致膜与水的润湿性大大增加。用椭偏仪和原子力显微镜(AFM)测量的水凝胶刷的溶胀度也证实了接枝网络的形成，并发现与单体进料中交联剂的量直接相关。此外，通过调节交联剂的浓度，调整了PAAM电刷和水凝胶电刷的杨氏模数和摩擦学性能。由于每个链端的表面拴系给出了额外的约束，分子间交联在刷子结构中产生了非常高的机械应力。因此，与接枝的聚合物刷子相比，共价交联水凝胶刷子具有更高的杨氏模数和摩擦系数。这些水凝胶刷子提供了轻松定制物理特性的机会，特别是当它们允许调整表面的物理特性时，同时保持界面化学成分几乎恒定。
Tethering macromolecules to surfaces represents a versatile approach for functionalizing, protecting, and structuring both organic and inorganic materials. In this study, thin films of poly(acrylamide) (PAAm) brushes and covalently cross-linked hydrogel brushes were grown from iniferter-functionalized silicon substrates by UVLED-initiated photopolymerization and their properties subsequently studied by means of a variety of analytical methods. The employed photografting method allowed the controlled fabrication of very thick films (up to 1 mu m) in an aqueous environment, over a period of less than 1 h of polymerization and in the absence of side reactions. PAAm covalently crosslinked hydrogel brushes were prepared by feeding trace amounts of the crosslinker bis(acrylamide) (up to 1.0 wt % of monomer solution) into the reaction vessel. Both bulk and interfacial properties of these polymer films were found to be strongly influenced by lateral cross-linking of the grafted polymer chains. In agreement with theoretical expectations, the decrease of polymer-brush conformational freedom with increasing cross-link density resulted in a substantial increase of film wettability with water. The swelling ratio of the hydrogel brushes, as measured by ellipsometry and atomic force microscopy (AFM), also confirmed the formation of grafted networks and was found to be directly related to the amount of cross-linker in the monomer feed. In addition, the Young's moduli and tribological properties of PAAm brushes and hydrogel brushes were tuned by adjusting the cross-linker concentration. Because of the additional constraint given by the surface tethering of each chain end, intermolecular cross-linking generated very high mechanical stresses within the brush structure. Covalently cross-linked hydrogel brushes thus displayed higher Young's moduli and coefficients of friction, when compared to the grafted polymer-brush analogues. These hydrogel brushes present an opportunity for readily tailoring physical properties, especially as they allow tuning of the physical characteristics of surfaces while maintaining the interfacial chemical composition nearly constant.